This invention involves the use of an image dye-forming coupler which releases a dye or dye precursor as the coupling off group. These are called "High Dye-Yield" (HDY) couplers because they form two molecules of dye for each molecule of coupler which is consumed.
Useful high dye-yield couplers have been disclosed by Mooberry and Singer in U.S. Pat. 4,840,884. (The '884 patent) Such couplers react with oxidized color developer to form one dye and in doing so release a precursor of a second dye having a neutral dye chromophore. In accordance with the patent, the new couplers described therein enable lower concentrations of silver halide in the photographic element without lowering image quality.
Large, high speed silver halide emulsions coated on a support, particularly those with a tabular morphology, are sensitive to fog formation caused by pressure events. These pressure events can arise from the film being tightly wound around a spindle in a film cartridge, or from contact with rollers and other surfaces during its manufacture and use, or from any bending of a flexible support bearing such an emulsion through a severe radius of curvature.
Various ways are known in the art by which the film structure may be modified or by which the sensitive emulsion may be modified to reduce the pressure sensitivity. For instance, the incorporation of pressure absorbing layers in the top of the film pack is well known. The inclusion of hydroquinones in such layers is taught in DD293207, EP476,521 and 482,599. Polymeric inclusions are described in U.S. Pat. No. 4,895,791. While these methods offer good reduction in pressure fog etc, they add material to the upper layers of the film material. This means that those layers are thicker and so there is a concomitant reduction in the sharpness and developability of underlying layers. Modifications to the structure of the silver halide emulsions to reduce pressure sensitivity are also known. For example, EP 295,439 and EP 299,719 describe the preparation of emulsions with low pressure sensitivity, and EP 517,901 describes an emulsion surface treatment to reduce pressure sensitivity. It is also possible to release antifoggants in the layer to reduce sensitivity (eg. EP 468,104). These methods lead to changes in the structure, speed, or developability of the emulsion and so they can adversely affect its performance.
Current trends are toward the miniaturization of cameras and the film employed to record the image. These trends may be served through the utilization of film which is smaller in format and/or is more tightly wrapped than is the case with conventional cameras and film. Thus, the desired miniaturization is dependent on a photographic element which can withstand a tight wrapping about the film spool without undue increase in pressure fog.
It is a problem to be solved to provide a tightly wrapped photographic element which exhibits less pressure sensitivity than conventional elements while maintaining satisfactory photographic response.